The present invention relates to an electric power steering system for an automobile.
A typical example of electric power steering systems has been proposed already in Japanese Utility Model Laid-open Publication No. 60 (1985)-188,064, for example, in which the front wheels are steered by transmitting the torque of a steering wheel shaft to a steering gear box assembly. In this known electric power steering system, the torque of an electric motor is transmitted to the steering wheel shaft through a freewheel clutch to reduce steering effort of the driver.
In such an electric power steering system, main parts of an assisting unit, such as the electric motor, an electromagnetic clutch and a torque sensor, are integrally mounted to the steering shaft, and these main parts are electrically connected to a control unit, which is mounted to a dashboard of the automobile, via cables and couplers.
The operation of this known electric power steering system cannot be tested until the control unit is connected to the main parts of the assisting unit by means of cables and couplers. Moreover, there is a possibility that the reliability of the electric power steering system decreases due to imperfect electrical contact.
It is an object of the present invention to overcome the disadvantages above described.
It is another object of the present invention to provide an electric power steering system which facilitates reduction in size thereof.
It is still another object of the present invention to provide an electric power steering system which facilitates mounting thereof to the automobile.
In view of these and other objects, the present invention provides an electric power steering system for an automobile having a steering shaft assembly with a steering torque transmitting shaft, comprising: a housing mounted on the steering torque transmitting shaft; a torsion torque sensor, provided in the housing, for detecting a torsion torque on the steering torque transmitting shaft during a steering operation to generate a torsion torque signal representing the detected torsion torque; an electric motor mounted on the housing and operatively connected to the steering torque transmitting shaft; and a controlling unit, integrally mounted to the housing and responsive to the torsion torque signal for providing a drive signal to control the electric motor so as to reduce steering effort.